Herpes Simplex Virus

September 14, 2011

Herpes simplex virus type I (HSV-I) and herpes simplex virus type II (HSV-II) are closely related viruses that cause two distinct clinical syndromes, with some overlap in the roles of the two viruses in each syndrome. Infection with HSV-I causes oral lesions (“cold sores,” although not all cold sores are due to HSV-I) and is transmitted by saliva, most commonly by kissing or a shared drinking glass. HSV-II is a sexually transmitted virus that produces genital lesions. There is some overlap, with less than 5% of oral HSV caused by HSV-II and about 5% of genital HSV produced by HSV-I. In both cases, the signature lesions of infection are small vesicular (bubble-like) lesions filled with clear fluid that appear singly or in clusters. Like other members of the herpesvirus family, infection with HSV-I and II is lifelong, with dormant infection followed by recurrences common.

Genital infection with Herpes simplex virus is one of the three most common sexually transmitted diseases in the United States (with chlamydial infection and human papillomavirus infection). Genital herpes produces more emotional distress than significant medical consequences. Many cases are asymptomatic and the prevalence of infection in the general population approaches 25%.

Genital herpes is more common in women than men, infecting approximately one out of four women versus one out of five men. This difference in gender may be because male-to-female transmission is more efficient than transmission from females to males. About 26% of sexually active young women have evidence of exposure to HSV-II on blood tests of prior exposure to genital herpes.

Many individuals never have any signs or symptoms. When signs and symptoms do occur, they typically appear as one or more blisters on or around the genitals or rectum. The blisters break, leaving tender ulcers (sores) that may take 2-4 weeks to heal the first time they occur. The first episode usually occurs within 2 weeks after the virus is transmitted, and the sores typically heal within 2-4 weeks. Other signs and symptoms during the primary episode may include a second crop of sores or flu-like symptoms, including fever and swollen glands. Occurrences are not uncommon, but are almost always less severe and shorter than the first episode. The pattern of subsequent outbreaks of genital herpes is highly variable. Individuals may have no recurrences, one every year, or several per year. Although the HSV-II virus stays in the body indefinitely, the number of outbreaks tends to go down over a period of years. Individuals with frequent outbreaks of genital herpes can take prophylactic medicine to prevent outbreaks (see below). HSV-II infection can be severe in people with suppressed immune systems. Active genital HSV-II lesions can enhance the transmission of HIV, and may alter the progression of HIV disease.

Herpes simplex virus type II can produce potentially fatal infections in infants if the mother is shedding virus at the time of delivery. It is important that women avoid contracting herpes during pregnancy because a first episode during pregnancy causes a greater risk of transmission to the newborn. If a woman has active genital herpes at delivery, a cesarean delivery is usually performed. Fortunately, neonatal infection with HSV-II is rare.

Individuals with active lesions are very contagious and should avoid sexual contact during an outbreak. HSV-II is shed in very small amounts between symptomatic outbreaks and individuals with no active lesions can pass on the virus to a sexual partner, although the risk is very low. Even individuals with no symptoms of HSV-II can be contagious, but the risk per sexual encounter is very low. Occasionally one member of a monogamous pair will come down with a symptomatic case, having contracted the infection from his/her partner who may be an asymptomatic carrier. Because the risk per sexual encounter is low, this sometimes occurs after many into a relationship, and can lead to great consternation among the partners. When this occurs, it is essential for the health care provider to know and effectively communicate that HSV-II can be contracted from long-time asymptomatic partners.

The diagnosis of genital herpes can be made by visual inspection if the outbreak is typical, and by taking a sample from the sore(s). Blood tests can be used to confirm the diagnosis in atypical cases or in diagnosing asymptomatic infection.

There are a number of antiviral medicines that are effective in treating HSV-II, including acyclovir, valacyclovir, and famciclovir. These may be used in treating outbreaks; the benefit in terms of reducing the severity and duration of genital herpes is greatest for the first outbreak when patients are most symptomatic. The benefit in treating recurrences is more modest, but when the medicines are taken daily they are very effective in preventing recurrences.

The consistent and correct use of latex condoms can help protect against infection. However, condoms do not provide complete protection because the condom may not cover the herpes sore(s), and viral shedding may nevertheless occur. A vaccine for HSV-II is under development.

Oral lesions due to HSV-I have a similar natural history to genital lesions due to HSV-II and the therapeutic and preventive strategies are similar. Patients with many frequent recurrences may benefit from preventive therapy.